1. Field of the Invention
This invention relates to an apparatus for detecting and displaying a supplementary program contained in a television program that is currently being transmitted and, more generally, it relates to a technology of detecting the status of reception of data transmission signals for characters and graphics contained in television signals for the sake of television viewers.
2. Description of the Related Art
The multiplexed text broadcasting, or teletext, is a currently available television broadcasting service for transmitting signals for characters and graphics along with ordinary television signals through a single transmission channel. It is used currently for programs of various categories including news, weather forecast, traffic information, tourism information and television shopping. In some programs, teletext is used for television polling.
The teletext is unilateral in the sense that information is offered only from the broadcasting station to the viewers. In the case of a telephone shopping program where the program provider transmits shopping information utilizing teletext, each viewer may take a memo of the code of each commodity he or she wants to buy, the telephone number of the mail-order firm and other pieces of information displayed on the screen and may subsequently dial the telephone number for ordering by referring to this memo. In the case of a program for television polling, viewers will also take a memo of the telephone numbers to be used for the poll and subsequently dial one of the telephone numbers by referring to the memo. In either case, however, there arises a problem that viewers can dial a wrong number because of a wrong dialing operation, whether because a wrong number has been memoed or for some other reason.
Thus, firstly, since the teletext is unilateral in the sense that information is offered only from the broadcasting station, the need to wait for calls from viewers create a long response time. Secondly, if the process entails telephone calls, it intrinsically involves wrong calls that will take place with a certain probability.
In order to bypass the above identified problems, there has been proposed a technique by which the broadcasting station transmits computer program data to each computer receiving set having the teletext feature. This technique comprises a means for executing a computer program by using the transmitted data so that the computer program executing means automatically dials the transmitted telephone number when the viewer keys in the command for such a call and also transmits other data keyed in by the viewer. With such an arrangement, the probability of dialing a wrong number is reduced to nil and the response time is significantly curtailed. In the following description, the program in which computer program data and supplementary data on characters and graphics explain the proper television program will be referred to as the supplementary program and the computer program will be referred to as script.
Since most of the existing circuit block (teletext transmission decoder) for receiving and processing teletext programs can be shared by the circuit block (data transmission decoder) for receiving and processing supplementary programs, the combination of a teletext transmission decoder and a data transmission decoder can be dimensionally reduced when they are designed in the form of a single circuit block that is operated selectively either in a teletext program mode or in a supplementary program mode.
When a circuit block adapted to both supplementary programs and teletext programs is operated in the supplementary program mode, it is of vital importance that the viewer can visually ascertain if the output of the circuit is being displayed or not in order to avoid a misguided action on the part of the viewer.
If the supplementary program is being transmitted simultaneously with the proper program, for example, and the viewer misunderstands that the supplementary program is not being transmitted, the viewer cannot respond correctly to the supplementary program by accessing it in a proper manner.